diff --git a/generate_pa11y_ci_urls_from_git_diff.sh b/generate_pa11y_ci_urls_from_git_diff.sh
index 66a2c8ba2f..41dae31a41 100644
--- a/generate_pa11y_ci_urls_from_git_diff.sh
+++ b/generate_pa11y_ci_urls_from_git_diff.sh
@@ -2,6 +2,7 @@
 # Take in a base ref. Gets the files that have changed from the base to the HEAD.
 # Export the list as a CommonJS module for the pa11y-ci configuration to use.
 # Typical usage: generate_pa11y_ci_urls_from_git_diff.sh gh-pages > .pa11yci.js
+# Assumes git is installed and on the path.
 
 function generate_pa11y_ci_urls_from_git_diff {
   base_ref=$1